Wordpress Login is a Wordpress plugin that will allow users to register into a Wordpress website with a Twitter account in one single click.

See Wordpress with Twitter account Full Documentation for full documentation

1. Download the plugin and upload it to your plugins folder as you would do with any other Wordpress plugin

2. Create a new app at Twitter here

3. Copy the Consumer Key and Consumer Secret and paste them in twitterlogin.php

4. Change the $salt variable to something long and complicated

5. Optionally, you can change the username prefix to something else to increase security

To see if a user is logged in through Twitter run is_user_logged_in() and then check if the username matches the Twitter prefix (tw- by default).

To retrieve the current user's data do something like this:

global $current_user;
get_currentuserinfo();
echo 'Hello ' . $current_user->nickname;
echo 'User token: ' . $current_user->oauth_token;
echo '<img src="' . $current_user->profile_image_url . '" alt="" />';

To retrieve data from someone else do something like this:

$user_info = get_userdata($user_id);
echo 'Username: ' . $user_info->nickname;

More information at Wordpress with Twitter account Full Documentation.